1. Field of the Invention
The present invention relates to drilling fluids utilized in the drilling of subterranean oil and gas wells. In particular, the invention relates to a surfactant for use in invert emulsion, or preparing water-in-oil emulsion, drilling fluids and the method of their use.
2. Brief Description of the Prior Art
It is generally agreed among those skilled in the art that a rotary system is the most acceptable form of drilling a subterranean well. This system depends upon the rotation of a column of drill pipe to the bottom of which is attached a multi-pronged drilling bit. The bit cuts into the earth, causing the cuttings to accumulate as drilling continues. As a result, a drilling fluid must be used to carry these cuttings to the surface for removal, thus allowing the bit to continue functioning, and the bottom hole to be kept clean and free of cuttings at all times. Drilling systems other than the rotary system are sometimes employed in drilling operations. Nevertheless, these systems still require a drilling fluid to remove borehole cuttings, and to otherwise perform functions related to drilling fluids. In many instances, what is generally referred to as a "drilling fluid" actually may be utilized, with either no modification, or only minor modification, as a fluid for use in conjunction with completing or working over a subterranean well. In this regard, utilization of the phrase "drilling fluid" herein contemplates the utilization of such fluid in such completion and workover operations in subterranean wells, as well as in drilling operations.
Although aqueous-based drilling fluids which utilize clear water, brine, saturated brine, or sea water as the primary liquid base, may be found to be dominant within some facets of the drilling industry, there is a considerable need for drilling fluids wherein a hydrocarbon liquid forms the major liquid constituent, particularly in instances in which the drilling fluid is utilized in the higher temperature wells which are drilled to the more substantial depths.
Hydrocarbon-based drilling fluids normally are defined as invert emulsion, or water-in-oil emulsion, drilling fluids. These emulsions provide droplets of water which typically are dispersed in a continuous phase of oil. The oil, or continuous phase, typically will comprise a hydrocarbon, such as mineral oil, diesel oil, crude oil, kerosene, or the like. The amount of oil used typically will be within the range of about 60 to about 95 parts by volume, and preferably within the range of about 70 to about 90 parts by volume, on the basis of 100 parts equalling the liquid phase of the drilling fluid. At the higher level of the range, a drilling fluid with a comparatively lower viscosity will be produced, while drilling fluids having a lesser amount of oil will produce a comparatively higher viscosity fluid. The concentration of the selected hydrocarbon depends upon the particular application for which the water-in-oil drilling fluid is to be utilized.
The dispersed liquid phase of the drilling fluid is normally referred to as the "water phase" and may consist of fresh water, salt water, sea water, or saturated brine. Normally, the presence of typical amounts of sodium chloride, calcium chloride, calcium carbonate, or calcium sulphate salts will have little significant effect on the stability of the emulsion which is typically produced. The water concentration should be in the range from between about 5 to about 40 parts by volume, and, typically, will be within the range of about 10 to about 30 parts by volume, on the basis of 100 parts equalling the liquid phase of the drilling fluid composition. Again, the exact concentration depends upon the particular application for which the invert emulsion drilling fluid is to be utilized.
Imidazoline-containing compositions long have been commercially utilized as wetting agents in shampoos and soaps. For example, imidazoline salts are disclosed for utilization in such compositions in U.S. Pat. No. 3,071,590, entitled "Condensation Products of Formaldehyde, Primary Amines and Ketones". Additionally, imidazolines, such as those taught in U.S. Pat. No. 3,654,177, entitled "Emulsifier Composition" have been found to be useful in preparing emulsifiers for certain water-in-oil emulsions for cutting oils, hydraulic fluids, lubricants, cosmetics, agricultural emulsions, and in invert drilling fluids for subterranean wells. Similar materials also are disclosed in U.S. Pat. No. 2,999,063, entitled "Water-in-Oil Emulsion Drilling and Fracturing Fluid".
When a polyamine and a fatty acid are reacted at temperatures of about 180.degree. C., and water extraction permits ring closure, the reaction is driven to completion and an imidazoline intermediate or final product (depending upon further stages in the reaction) is produced. If the reaction is conducted at somewhat reduced temperatures of between about 160.degree. C. to about 175.degree. C. and approximately one mole of water is distilled for each mole of fatty acid introduced into the formulation, ring closure will be prevented, and an amide will be produced, as opposed to a true imidazoline, or an imidazoline in conjunction with numerous reaction mixtures. Accordingly, when utilized herein, the word "diamide" contemplates the reaction of a polyamine with approximately two moles of fatty acid at such temperature and under such conditions that the total reaction required to form a product with complete ring closure is not complete and an imidazoline or imidazoline and reaction product mixtures, are not formed. Those skilled in the art can easily prepare a diamide, such as that disclosed in U.S. Pat. No. 3,134,759, entitled "Tall Oil Amide for Inhibiting Corrosion," which teaches the preparation of such amides as well as their use as a corrosion inhibitor.
Hydroxyethylacetamides and ethoxylated hydroxyethyl acetamides have been utilized as emulsifiers in water-in-oil drilling fluids, as shown in U.S. Pat. No. 3,125,517, entitled "Invert Emulsion Drilling Fluid."
Certain imidazoline salts have also been suggested for use in drilling fluids. For example, U.S. Pat. No. 3,514,399, entitled "Drilling Fluids Containing Imidazoline Salts," discloses the use of a mixed dimer acid-monocarboxylic acid salt of an imidazoline in drilling fluids as a borehole stabilizer.
Certain amines and amides within specific reactions have also been disclosed and utilized in water-in-oil emulsion drilling fluids, such as U.S. Pat. No. 3,041,275, entitled "High Temperature Emulsion Drilling Fluid." Finally, certain polyamides without the incorporation of an acid, particularly without an incorporation of a tricarboxylic acid, have been utilized as water-in-oil emulsion fracturing fluids, such as in U.S. Pat. No. 3,169,113, entitled "Emulsifier Compositions and Uses Thereof."
It has been found that a more economical, more stable water-in-oil surfactant will result from the preparation and utilization of a surfactant composition comprising: from between about 20 mole percent and about 35 mole percent of a polyamine; from between about 30 mole percent and about 70 mole percent of a fatty acid having from between about 6 carbon atoms and about 20 carbon atoms therein, and from about 15 mole percent to about 35 mole percent of a tricarboxylic acid.
It should be noted that the composition of the surfactant will always be expressed in terms of the total formulation. When the end product is diluted to 70 w/w percent concentration with a suitable solvent, the surfactant will have an acid value of from between about 26 to about 46, and a total amine value of from between about 10 to about 30. Again, all acid and amine values are given to 70 w/w percent solutions of the surfactant.
The electrical stability of the emulsion produced with the surfactant will exceed about 400 volts at ES.sub.3 as defined hereafter, and ES.sub.5 will be greater than ES.sub.4, the ES.sub.5 being greater than about 1,000 volts. Alternatively, the electrical stability of an emulsion drilling fluid, when using the API Electrical Stability Test should be at least about 1,000 volts.